Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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987 FXUS63 KMPX 301134 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 634 AM CDT Tue Apr 30 2024 .KEY MESSAGES... - Slight Risk (Level 2 of 5) of severe weather across south central Minnesota this afternoon for the next round of showers & thunderstorms. The main threats are damaging wind and large hail, along with the chance for an isolated tornado or two. - Unsettled weather pattern continues, with multiple chances for rain in the upcoming forecast. The next round of widespread rain will be Thursday, followed by additional rain chances Saturday and again early next week. && .DISCUSSION... Issued at 340 AM CDT Tue Apr 30 2024 The dreary Monday weather is exiting stage left this morning, as the surface low has now drifted into northern Wisconsin. Latest observations reveal the mist/drizzle has lifted north and all that is left is a slow moving layer of stratus. This cloud layer will continue to drift eastward over the coming hours. Winds have become light following the departure of the surface low and forecast soundings have hinted at the potential for some patchy fog developing across central Minnesota. Any fog that develops will mix out of the picture as southeasterly winds increase today, ahead of the next round of active weather. Our attention remains focused on a potent shortwave trough that is captured on GOES water vapor imagery as it begins to advance east of the Rockies. Ahead of this feature is a mid-level thermal ridge, which will will be a key player in a notable warm-up on tap heading into this afternoon. The latest forecast calls for highs in the 60s to low 70s across the area. Following a dry and warm period for much of the day, the focus will shift to an incoming line of rain and thunderstorms. The shortwave trough is progged to slide to the east of the Dakotas this afternoon, becoming negatively tilted as it lifts northeast through Minnesota. Strong diffluence will aid in creating broad ascent east of the trough. A line of showers and thunderstorms will develop east of the this feature as the trough interacts with the wing of ongoing warm/moisture advection. CAM guidance is in stellar agreement with the expected evolution of today`s convective event, likely due to the synoptic nature of the forcing. Starting early this afternoon, a line of convection will move into western Minnesota. The line of storms will continue east into the evening, with the leading edge set to cross I-35 around 00z. Showers and storms will then persist east into western Wisconsin and should end shortly before midnight. Not many changes to report with the latest Day 1 outlook from the SPC, as a Slight Risk for severe weather remains in place across the southern 3 tiers of counties in Minnesota. Forecast soundings across this area depict an environment that is very much in the character of a low CAPE/high shear event, given the expected 500-1000 J/kg of MLCAPE and ~50 knots of 0-6km bulk shear. While instability will be lacking, low- level curvature in the hodographs indicates an atmosphere that will be capable of producing severe weather. Damaging winds and large hail will serve at the primary threats, however we cannot rule out an isolated tornado or two given the forecast wind profiles. It`s reasonable to say the expected "scattered" nature to the severe weather threat is likely the ceiling for this event given the stable lapse rates aloft and lack of moisture (forecast dew points reach the mid 50s along I-90). HREF guidance supports the idea that limited instability will put a lid on the overall threat, with a greater signal for much stronger updrafts to the south in Iowa. A Marginal Risk remains in place roughly to I-94 in Minnesota and Wisconsin. While we cannot rule out an isolated instance of damaging wind or hail in the Marginal Risk area, the presence of only a few hundred joules of MUCAPE should significantly limit the severe weather potential (including in the Twin Cities Metro). Rainfall amounts between 0.5" to 0.75" remain the expectation for most locations, though the HREF LPMM QPF parameter illustrates the possibility of higher amounts given convection/training. Dry weather returns for much of Wednesday and the temperatures will remain mild, with highs in the 60s across south central Minnesota and western Wisconsin. Of course, it`s only fitting that we "Rinse and Repeat" again on Thursday, as the next storm system of interest brings the return of widespread soaking rains and cooler temperatures. The latest global ensemble suite indicates that the storm may track a bit further to the southeast when compared to the last three storm systems. This would mean that most, if not all of the forecast area is on the cooler side of the storm and as a result, severe weather is not expected locally at this time. Early indications are that another half inch to inch of rain may fall from early Thursday through Friday morning, which is supported by forecast PWATs well into the 90th percentile of sounding climatology. The forecast will dry out again on Friday, but the departure of the Thursday storm system and yet another disturbance on Saturday will make for a breezy end of the work week. Speaking of the disturbance on Saturday, it does not look like the type of weather system that could produce soaking rains, rather scattered showery type precip for the first half of the weekend. Perhaps it comes as no surprise that another, yes... another more notable storm system will move through the Upper Midwest early next week and the early read from the ensemble suite is that we could be looking at a fifth widespread soaking rain event (dating back to this past Friday). The new NBM output features "likely" PoPs for the Monday/Tuesday system. It does not look like we are taking a break from needing the umbrella anytime soon... && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 623 AM CDT Tue Apr 30 2024 Model agreement remains high on timing of a line of storms across the area this afternoon and evening. As a result, only minor changes were needed to the going TAFs, mainly to try and narrow down TS windows at each terminal. There is some more uncertainty with how cigs will track post storms, as both the RAP and LAV have been trending toward holding post frontal stratus in at AXN/STC/MSP/RNH/EAU well into Wednesday morning, though we`re a little skeptical of cigs hanging around much after the fropa given the strong subsidence we will see in the wake of the wave kicking off the showers and storms. For winds, there will be a pretty abrupt switch from the southeast over the west with the fropa. KMSP...One trend we`ve been watching with the HRRR is its development of a shield of showers out ahead of the main line of storms, with some indications of -RA being possible as early as 20z. 23z-02z continues to look like the most likely window for seeing TSRA at MSP. Besides the threat for storms, there will be a very rapid switch in wind direction from the southeast over to the west with the fropa that will occur between 1z and 3z. /OUTLOOK FOR KMSP/ WED...VFR. Wind WNW 10-15 kts. THU...MVFR/-ShRA. Chc IFR. Wind E 10-20G30 kts. FRI...VFR. Wind W 10-15G25kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...Strus AVIATION...MPG